Stem cells are a population possessing 1) self-renewal capacity, 2) long-term viability, and 3) multilineage potential.
The multilineage potential of embryonic stem cells and adult stem cells from the bone marrow has been characterized extensively. Although embryonic stem cell potential is enormous, many ethical and political issues accompany their use. Therefore, adult stem cells from the bone marrow stroma (i.e., mesenchymal stem cells, MSCs) have been proposed as an alternative source.
Originally identified as a source of osteoprogenitor cells, MSCs differentiate into adipocytes, chondrocytes, osteoblasts, and myoblasts in vitro (Hauner et al., 1987; Grigoradis et al., 1988; Wakitani et al., 1995; Ferrari et al., 1998; Johnstone et al., 1998; Pittenger et al., 1999) and undergo differentiation in vivo (Benayahu et al., 1989; Bruder et al., 1998a), making these stem cells promising candidates for mesodermal defect repair and disease management.
However, the clinical use of MSCs has presented problems, including pain, morbidity, and low cell number upon harvest. This has led many researchers to investigate alternate sources for MSCs.
Adipose tissue, like bone marrow, is derived from the mesenchyme and contains a supportive stroma that is easily isolated. Based on this, adipose tissue may represent a source of stem cells that could have far-reaching effects on several fields.
Applicant has identified a putative stem cell population within human lipoaspirates. This cell population, called processed lipoaspirate (PLA) cells, can be isolated from adipose tissue in significant numbers and exhibits stable growth and proliferation kinetics in culture. Moreover, PLA cells, like MSCs, differentiate in vitro toward the osteogenic, adipogenic, myogenic, and chondrogenic lineages when treated with established lineage-specific factors.
Based on the multilineage differentiation capacity of PLA cells, Applicant recognized that a population of multipotent stem cells, comparable with MSCs, can be isolated from human adipose tissue.
When collecting human adipose tissue, usually a compound of a liquid fraction and a dense fraction of the adipose tissue is gathered.
Up to now, regenerative cells of the adipose tissue are recovered starting from the collected dense fraction: the collected compound is first filtrated in order to separate the dense fraction from the liquid fraction, the latter being usually discarded.
Subsequently, the dense fraction is added with specific reagents (e.g. enzymes).
After a reaction time usually lasting around 30 to 60 minutes, the digested dense fraction of the adipose tissue is subjected to centrifugation which leads to the separation of the different phases (adipose portion and fluid portion) of the dense fraction and to the precipitation of a pellet rich of regenerative cells.